I. FIELD OF THE INVENTION
present invention relates to a novel process for the preparation of a supported catalyst for the polymerization of .alpha.-olefins in which
(1) a silicon dioxide-containing support gel is prepared by PA1 (2) the support gel (1) is charged with chromium trioxide oxide or a chromium compound which can be converted into chromium trioxide under the conditions of process step (3), giving a chromium-containing support gel, and PA1 (3) the chromium-containing support gel (2) is heated at from 400.degree. to 1100.degree. C for from 10 to 1000 minutes in an anhydrous gas stream containing oxygen in a concentration of greater than 10% by volume. PA1 (1) a silicon dioxide-containing support gel is prepared by PA1 (2) the support gel (1) is charged with chromium trioxide or a chromium compound which can be converted into chromium trioxide under the conditions of process step (3), giving a chromium-containing support gel, and PA1 (3) the chromium-containing support gel (2) is heated at from 400.degree. to 1100.degree. C for from 10 to 1000 minutes in an anhydrous gas stream containing oxygen in a concentration of greater than 10% by volume,
(1.1) introducing a sodium water glass or potassium water glass solution into a swirling stream of an aqueous mineral acid longitudinally and tangentially to the stream, spraying the resultant silica hydrosol in drop form into a gaseous medium and allowing it to solidify to form a hydrogel, and freeing the resultant hydrogel from salts by washing without prior ageing, PA2 (1.2) drying the hydrogel resulting from (1.1) to form the support gel, PA2 (1.1) introducing a sodium water glass or potassium water glass solution into a swirling stream of an aqueous mineral acid longitudinally and tangentially to the stream, spraying the resultant silica hydrosol in drop form into a gaseous medium and allowing it to solidify to form a hydrogel, and freeing the resultant hydrogel from salts by washing without prior ageing, PA2 (1.2) drying the hydrogel resulting from (1.1) to form the support gel,
The present invention furthermore relates to a novel supported catalyst for the preparation of polymers of .alpha.-olefins which is obtainable by the novel process, and to the .alpha.-olefin polymers prepared with the aid of this novel supported catalyst.
II. Description of Related Art
The abovementioned process for the preparation of a supported catalyst for the polymerization of .alpha.-olefins is disclosed, apart from the improvement according to the invention, in EP-A 0 429 937. It is essential for this known process that the hydrogels resulting from step (1.1) are dried at a maximum of 180.degree. C. under a reduced pressure of 13.3 mbar until no further weight loss occurs. Drying times of several hours are necessary for this purpose.
Furthermore, DE-A 41 32 894 likewise discloses a process for the preparation of a supported catalyst for the polymerization of .alpha.-olefins, in which the drying time of the support gels necessary for the preparation of the supported catalyst can be reduced to a few seconds. The drying here is carried out in a high-speed dryer at an inlet temperature of from 200.degree. to 600.degree. C. Supported catalysts prepared in this way can be used to give .alpha.-olefin polymers having improved low-temperature toughness and processing properties.
The drying methods described in EP-A 0 429 937 and DE-A 41 32 894 for the preparation of the support gels do not involve shaping, and the resultant supports are consequently obtained either as splintery fragments of expanding hydrogel (EP-A 0 429 937) or as particles of undefined morphology (DE-A 41 32 894), which must subsequently be ground. The particles having sizes of less than 30 .mu.m obtained from this grinding process are undesired in the polymerization process since they are responsible for the formation of fine polymer dust. In order to eliminate this fine dust, which makes up about 20% of the entire amount of support, it must be separated off by screening and subsequently discarded, which involves a not inconsiderable increase in the process complexity.